1. Field of the Invention
The present invention relates to a tape attached on the inner side of the seam of a food product packaging container made of paper-based ply material blanks an improvement in the barrier feature in the seam area.
2. Prior Art
It is known that there is a food product packaging container for liquid food such as milk, juice, or the like, which is airtight by sealing off the top and bottom open ends of a tube-shaped ply material made of paper-based ply board blank by folding and overlapping the lengthwise end portions for welding to form a seam.
In such an airtight packaging container having a seam B as shown in FIG. 4, the lengthwise end surface a of the ply material A' is exposed along the seam B. It is recognized that the exposed ply material may not satisfy the requirement of food sanitation laws which prohibit the contents of the container from coming into direct contact with any substance except for polyethylene, by generally overlapping and welding the lengthwise end portion of the play material A'.
In the prior art, a tape strip S covering the inner side of the seam B as shown in FIG. 4 exists (for example, that disclosed in Japanese Patent Publication No. 56-14544).
The object of invention of the above-identified application is to protect a tape strip from deforming by heat. However, there is no explanation on a barrier protection against water, gases, and most seriously against oxygen and light. Accordingly, in whatever manner the tape strip S is attached to the inner side of the seam B, oxygen and other substances may enter into the airtight container A through the seam B. For example, although the container A is airtight, oxygen may enter it through a paper base layer 1 as indicated by the arrow in FIG. 4 and can move inwardly across the tape strip S eventually coming into direct contact with the food product in the container A.
Since the permeability of gases, including oxygen, is greater in the tape strip S than in the ply material A', gases entering from the seam B always pass through the tape strip S to finally come into direct contact with the contents of the container A. Consequently, when impurities enter the airtight container A, the food product in the container A deteriorates.